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4.1 Introduction to water systems - Coggle Diagram
4.1 Introduction to water systems
Earths Water Budget:
Blue planet (70% of Earth’s surface is water).
97% is salt water and only 2.6% is fresh water.
Fresh water only makes up a small fraction (approximately 2.6% by volume) of the Earth's water storages.
The water cycle
Over 2/3rds of the earth’s surface is covered with water, but less than 1% is fresh water for drinking.
Fresh water is a scarce resource and is fast becoming a political issue in the developing world.
Flows in the hydrological cycle include evapotranspiration, sublimation, evaporation, condensation, advection (wind-blown movement), precipitation, melting, freezing, flooding, surface run-off, infiltration, percolation and stream-flow or currents
Human activities such as agriculture, deforestation, and urbanisation have a significant impact on surface run-off and infiltration
Human impact on the hydrological cycle:
Withdrawals: Domestic use, irrigation and industry
Discharges: Adding pollutants; sewage/fertilisers
Changing flow speed: Rivers are channelled underground; Canalising (straightening large sections); Dams/barrages/dykes
Diverting rivers: Away from important areas to avoid flood damage; Towards dams to improve storage
Human impact on water cycle
Ganges Basin
Aral sea:
Intense irrigation has almost stopped river flow into the sea. The sea level has lowered. The area of the Aral Sea has shrunk almost 90% in the last 50 years
Ocean circulation
Ocean circulation systems are driven by differences in temperature and salinity. The resulting difference in water density drives the ocean conveyor belt, which distributes heat around the world and thus affects climate.
Transports heat: equator to poles
Transport nutrients and organisms
Influences weather and climate
Influences commerce
Ocean Currents (horizontally and vertically)
Surface Currents: The upper 400 meters of the ocean (10%). Are moved by winds
Deep Water Currents: Thermal/Salinity currents (90%). When warm water rises, cold water goes down to replace it, and when cold water rises, warm water goes down to replace it).
Transport by currents:
Surface currents play significant roles in transport heat energy from equatorial waters towards the poles
Currents also involved with gas exchanges, especially O2 and CO2
Nutrient exchanges important within surface waters (including outflow from continents) and deeper waters (upwelling and downwelling)
Pollution dispersal
Impact on fisheries and other resources
Ocean currents and climate:
Water has a higher specific heat capacity than land.
Therefore takes longer to heat up/cool down.
This means land close to the oceans has a mild climate.
E.g. The warm gulf stream/north Atlantic drift gives Britain (and NW Europe) a moderate climate when we should have a subarctic climate.
Great Ocean Conveyor Belt
The Great Ocean conveyor Belt is the name for a model of the large system of ocean currents that affects weather and climate by circulating thermal energy around Earth.
In this model, high salinity water cools and sinks in the North Atlantic, and deep water returns to the surface in the Indian and Pacific Oceans through upwelling
Scientists estimate that the Great Ocean Conveyor Belt model takes about 1,000 years
El Niño-Southern Oscillation (ENSO)
El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around December
Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño
ENSO describes a combined oceanic-atmospheric disturbance
normal situation over Pacific Ocean (non-El Nino year):
low pressure over Asia
high pressure over South America
winds blow east to west most times of the year.
shallow thermocline along South (America, lots of upwelling, cold water at surface/Asia, warm surface water piles up)
Effects:
warm water with few nutrients rises
fisheries decline
increased precipitation over parts of South America, western and southern U.S.
can result in severe flooding
drought in Australia, Indonesia, Phillipenes
reduction in annual monsoons in India
can result in severe crop damage
severe property damage and thousands of deaths
La Nina
opposite El Nino
swings the other way and winds blow more than normal towards west